It really depends on what type of armour you are refering to.
I have seen some medieval full armour at musuems and from their construction seems restrictive.

Care to elaborate?

I have seen guys fight in full armour at demos and they appear quite sluggish.

Anything of that sort should not be taken as representational, since many reenactors are sorely lacking in the athletic department anyway.

I could understand flexiblity of chain mail armour, fish scale armour, small plate metal on leather armour. Even with chain mail its really heavy.

What's your definition of "really heavy"?

European plate armor is actually far less restrictive than people realize; maille rests predominantly on the shoulders (though the waist belt helps even things out a bit), whereas plate is much better distributed over the entire body.

A full field-harness (battlefield armor) will typically weigh in the 60-lb range, which compares favorably with Japanese lamellar armors, which can range anywhere from 55 to 77 lbs.

(Sources: The Medieval Soldier by Gerry Embleton and John Howe, and Classical Fighting Arts of Japan by Serge Mol.)

There's no evidence whatsoever that what we call boxing and wrestling now has any lineage relationship to the arts the Greeks and Romans practiced that we translate as boxing and wrestling. In fact, those sports owe quite a bit to the an earlier era of "reconstructing" Western martial arts by taking folk arts of no particular provenance and attaching them to rules sets patterned after tradition.

What interests me is that virtually all contemporary martial arts (East and West) seem to have been codified into current forms sometime from the 18th century onward.

There's no evidence whatsoever that what we call boxing and wrestling now has any lineage relationship to the arts the Greeks and Romans practiced that we translate as boxing and wrestling. In fact, those sports owe quite a bit to the an earlier era of "reconstructing" Western martial arts by taking folk arts of no particular provenance and attaching them to rules sets patterned after tradition.

Lineage-wise, I agree with you, though technique-wise, it's clearly more open--eg., techniques recognizable to any modern-day grappler may be seen in the Beni Hassan illustrations of c. 2000 B.C., as well as later Greek and Roman art.

What interests me is that virtually all contemporary martial arts (East and West) seem to have been codified into current forms sometime from the 18th century onward.

There's no evidence whatsoever that what we call boxing and wrestling now has any lineage relationship to the arts the Greeks and Romans practiced that we translate as boxing and wrestling. In fact, those sports owe quite a bit to the an earlier era of "reconstructing" Western martial arts by taking folk arts of no particular provenance and attaching them to rules sets patterned after tradition.

True. There is probably no direct historical link between the pugilism practiced in ancient Greece and Rome and the English "revival" of boxing in the 1800s.

However, this particular fighting style, although it did somewhat resemble boxing as it was later developed in England, was actually an evolution of the earlier Italian art of stick fighting, which was the original method used in the "bridge battles". It's difficult to demonstrate any linear historical connection between the Italian pugilism of this period and English boxing, and almost impossible to demonstrate a similar connection between ancient Greek or Roman boxing and the style that was developed by the bridge battlers.

We have many complete treatises on the arts of self defence as practiced throughout Europe during the Renaissance period, and although they demonstrate highly advanced martial arts for the use of the sword, dagger, unarmed combat, etc. there is very little (if anything) to suggest that boxing-style punching was emphasized in these arts.

Regarding the origins of modern "Greco-Roman" wrestling; during the late 1800s and early 1900s there was a wave of enthusiasm for classical studies throughout Europe, including developments in architecture, literature, the fine arts, dance and - oddly enough - athletics, all inspired by the examples of ancient Greece and Rome. One manifestation of this trend was the birth of the modern Olympic Games, which was originally just one of a number of similar sports festivals combining traditional European folk sports with varying degrees of "Greco-Roman re-enactment".

The French especially enjoyed re-constructions of ancient athletic events as a sort of "sports theater", almost like modern professional wrestling shows, and teams of actors and athletes would rehearse/train for weeks to put on a good performance. To quote wrestling historian Willie Baxter:

When the modern Olympic Games began in Athens in 1896, wrestling was one of the sports competed and like the other events the organisation was amateurish and the standard was very poor. The style of wrestling chosen was Greco-Roman, which despite its grandiose title owes nothing to Greece or Rome but everything to France.

The two Olympic styles are folk styles, which have been greatly technically developed since their Olympic inception, but the senior style, Greco-Roman, one of a family of Mediterranean styles, which have existed in La Provençe (South East France) since antiquity but was first formally codified in 1848 by a lawyer called Innocent Truquettil.

Greco-Roman was initially called in French la luttes à mains platte (open handed wrestling) and technical development began in the ‘athletes’ cafés’ of Lyon and Bordeaux. About 1860 it was sometimes referred to as la lutte Romaine (Roman wrestling) then later as la lutte Grecque (Greek wrestling). Eventually the two names were joined together and it became generally known as Graeco-Roman/Greco-Roman, though as late as 1910 it was frequently referred to in France as la lutte à mains platte.

Pierre de Fridi, Baron de Coubertin founder of the modern Olympic Games chose Greco-Roman for the first Olympic Games for several reasons, first because of the name which was chosen because the founders in 1848 genuinely believed that it was the type of wrestling described by Homer in the Iliad (circa 1200 BC). The second reason was because at that time it was the most popular spectator sport in Europe, excluding Britain where Catch-as-catch-can was incredibly popular.

To further clarify, at the time, Baron de Coubertin's selection committee was heavily influenced by the vogue for re-constructions of the ancient Games, and the co-incidence of styles between the native French open-handed wrestling and the styles represented in Classical art were overpowering. Had the French style not resembled what de Coubertin and his colleagues admired in representations of ancient wrestling, Catch-as-catch-can might well have received the Olympic nod, and the history of MMA, modern Olympic and collegiate wrestling, etc. might have been very different.

Lineage-wise, I agree with you, though technique-wise, it's clearly more open--eg., techniques recognizable to any modern-day grappler may be seen in the Beni Hassan illustrations of c. 2000 B.C., as well as later Greek and Roman art.

True enough, but there is also mention of these techniques on the other side of the world as well as techniques that are not used in Greco-Roman as much as in arts like Judo. I'd conclude that it's just a matter of people rediscovering effective techniques through experimentation.

When I think about the armor of earlier times, I can't help but wonder if a certain part of its utility (beyond simple athleticism) is simply the user being accustomed to it, much like the sorts of armor used today. For someone not used to it, a Kevlar helmet and vest are hot, uncomfortable, and inconvenient. After a few days/weeks/months/years of being worn, it's hardly noticed - the user learns to move "with" the armor, for lack of a better description. For all our difficulties in using earlier forms of armor today, is it due to a basic unfamiliarity with it?

Along the same lines we often draw conclusions based on examples on display in museums. How many of these examples are actual "user" pieces, and not simply works of art that are meant to be admired rather than used?

True enough, but there is also mention of these techniques on the other side of the world as well as techniques that are not used in Greco-Roman as much as in arts like Judo. I'd conclude that it's just a matter of people rediscovering effective techniques through experimentation.

It's interesting that you mention judo, if only because things like tomo-nage were employed by the Romans, even in battlefield situations (Cassio Dio mentioned the use of this technique by legionaries against barbarians on a frozen river, of all places...)

When I think about the armor of earlier times, I can't help but wonder if a certain part of its utility (beyond simple athleticism) is simply the user being accustomed to it, much like the sorts of armor used today. For someone not used to it, a Kevlar helmet and vest are hot, uncomfortable, and inconvenient. After a few days/weeks/months/years of being worn, it's hardly noticed - the user learns to move "with" the armor, for lack of a better description. For all our difficulties in using earlier forms of armor today, is it due to a basic unfamiliarity with it?

Probably.

European knights began their military training as children, and I imagine it was much the same with feudal bushi, et al. By the time these guys "went pro", they were certainly accustomed to it.

But again, it has to be stressed that armor was made not simply to be protective, but also to be functional--and, to satisfy the latter, it had to be well-designed.

Along the same lines we often draw conclusions based on examples on display in museums. How many of these examples are actual "user" pieces, and not simply works of art that are meant to be admired rather than used?

In the European context, the biggest problem in the past was confusing a battlefield armor ("field-harness") with an armor meant for jousting (i.e., a tournament armor). These jousting armors are often MUCH heavier than anything that was ever worn into battle--they should be viewed as highly specialized sporting equipment.